In the production of nonwoven spunbond web, a spinning head produces a curtain of filaments by extrusion of the thermoplastic synthetic resin from a multiplicity of orifices. The filaments cool as they emerge from the spinneret and, along their path toward a collecting foraminous belt are stretched between two nozzle-forming units which can be referred to as stretching nozzle units. Together these units form a passage in which the filaments are aerodynamically stretched.
The filaments are collected on the foraminous belt and produce thereon a web in which the jumbled filaments are bonded together. In the stretching nozzle, i.e. the nozzle gap between the stretching nozzle units, the filaments are subjected to entrainment with process air which is at a temperature above the ambient temperature. The processing air, for example, may have a temperature of 35° to 45° C. while the ambient temperature may be around 20° C. The two units described may, of course, be combined into a single stretching nozzle by being connected together at their ends. The spinneret and the stretching nozzle can extend across the width of the foraminous belt and the lengths of the spinneret and the stretching nozzle across the foraminous belt may correspond to the width of the nonwoven web which is produced.
Between the spinning head and the stretching nozzle there is usually a cooling stretch or cooling device for the filament and a suction system may be provided beneath the belt to promote collection of the filament on the belt.
Between the stretching nozzle and the belt itself there may be provided a filament deposition device which ensures the jumbling or matting of the stretched filament and their bonding together.
Such apparatus had proved to be highly successful for the production of nonwoven spunbond webs, although heretofore it has been found that the weight per unit area of the web may vary across the web and over the length thereof significantly. Such tolerances may be of the order of ±20%.
Such high tolerances in the weight per unit area distribution are undesirable.